Fuel processor feedstock delivery system

ABSTRACT

Fuel processing and fuel cell systems with feedstock delivery systems that are designed to deliver a mixed component feed stream to a hydrogen-producing region for the production of hydrogen gas therefrom and to selectively deliver the feed stream to a heating assembly for use as a combustible fuel stream for heating at least the hydrogen-producing region. The feed stream contains water and a carbon-containing feedstock, and may contain at least 31 vol % water. In some embodiments, the feedstock delivery system may be adapted to mix the components of the feed stream at a determined mix ratio and to deliver this feed stream to the fuel processor(s). The fuel processing system may also include one or more fuel cell stacks that are adapted to produce an electric current from the product hydrogen stream produced by the fuel processing system.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuing patent application and claims priorityto U.S. patent application Ser. No. 11/124,029, which was filed on May6, 2005, issued on May 6, 2008 as U.S. Pat. No. 7,368,195, and which isa continuation of and claims priority to U.S. patent application Ser.No. 09/893,357, which was filed on Jun. 26, 2001, and issued on May 10,2005 as U.S. Pat. No. 6,890,672. The complete disclosures of theabove-identified patent applications are hereby incorporated byreference for all purposes.

FIELD OF THE INVENTION

The present invention relates generally to fuel processing systems,which contain a fuel processor adapted to produce hydrogen gas, to fuelcell systems, which include a fuel processor and a fuel cell stack, andmore particularly, to an improved method and system for supplying amixed feedstock to a fuel processor.

BACKGROUND OF THE INVENTION

Fuel processing systems include a fuel processor that produces hydrogengas or hydrogen-rich gas from common fuels such as a carbon-containingfeedstock. Fuel cell systems include a fuel processor and a fuel cellstack adapted to produce an electric current from the hydrogen gas. Thehydrogen or hydrogen-rich gas produced by the fuel processor is fed tothe anode region of the fuel cell stack, air is fed to the cathoderegion of the fuel cell stack, and an electric current is generated.

In some fuel processors, the feedstock to the fuel processor includesonly a single component. Examples of these fuel processors includeelectrolysis units, in which the sole feedstock is water, and pyrollysisand partial oxidation reactors, in which the sole feedstock is ahydrocarbon or alcohol. In many fuel processors, however, the feedstockincludes more than one component, such as water and a carbon-containingfeedstock. Examples of carbon-containing feedstocks include an alcoholand a hydrocarbon. When the feedstock includes more than one component,these components need to be mixed and delivered to the fuel processor.Because the feedstock does not include a single component, the two ormore components forming the feedstock will be present in variouspercentages or fractions, with the relative mix of these percentagesaffecting the operation and/or efficiency of the fuel processor and themakeup of the product streams.

SUMMARY OF THE DISCLOSURE

The present invention is directed to a feedstock mixing apparatus forfuel processing systems, and fuel processing and fuel cell systemsincorporating the same. A fuel processing system according to thepresent disclosure includes one or more fuel processors adapted toproduce a product hydrogen stream from a feed stream containing waterand a carbon-containing feedstock. The fuel processing system furtherincludes a feedstock delivery system that is adapted to deliver a feedstream containing the feed stream to the fuel processor(s). The fuelprocessing system may also include one or more fuel cell stacks that areadapted to produce an electric current from the product hydrogen streamproduced by the fuel processing system. When the fuel processing systemincludes at least one fuel cell stack, it may be referred to as a fuelcell system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a fuel cell system with a feedstockdelivery system according to the present invention.

FIG. 2 is a schematic diagram of a fuel processor suitable for use inthe fuel cell system of FIG. 1.

FIG. 3 is a schematic diagram of another fuel processor suitable for usein the fuel cell system of FIG. 1.

FIG. 4 is a schematic diagram of a fuel cell stack suitable for use inthe fuel cell system of FIG. 1.

FIG. 5 is a schematic diagram of a feedstock delivery system accordingto the present invention.

FIG. 6 is a schematic diagram of another feedstock delivery systemaccording to the present invention.

FIG. 7 is a schematic diagram of another feedstock delivery systemaccording to the present invention.

FIG. 8 is a schematic diagram of another feedstock delivery systemaccording to the present invention.

FIG. 9 is a schematic diagram of another feedstock delivery systemaccording to the present invention.

FIG. 10 is a schematic diagram of another feedstock delivery systemaccording to the present invention.

FIG. 11 is a schematic diagram of another feedstock delivery systemaccording to the present invention.

FIG. 12 is a schematic diagram of a suitable controller for use with thefeedstock delivery systems of FIGS. 1 and 5-11.

FIG. 13 is a schematic diagram of a user interface for use with thecontroller of FIG. 12.

FIG. 14 is a schematic diagram of a fuel cell system including afeedstock delivery system with a controller according to the presentinvention.

FIG. 15 is a schematic diagram of a suitable reformer for use with thefeedstock delivery systems according to the present invention.

FIG. 16 is a schematic diagram of another suitable reformer for use withfeedstock delivery systems according to the present invention.

DETAILED DESCRIPTION AND BEST MODE OF THE INVENTION

A fuel cell system according to the present invention is shown in FIG. 1and generally indicated at 10. System 10 includes at least one fuelprocessor 12, at least one fuel cell stack 22 and a feedstock deliverysystem 26. In FIG. 1, a fuel processing system is also shown andgenerally indicated at 11. Fuel processing system 11 contains feedstockdelivery system 26 and at least one fuel processor 12 that is adapted toproduce a product hydrogen stream 14 from a feed stream 16 deliveredthereto by feedstock delivery system 26. As used herein, it should beunderstood that the term “fuel processing system” is used to refer to asystem adapted to produce hydrogen gas from a feed stream, and “fuelcell system” is used to refer to a fuel processing system in combinationwith at least one fuel cell stack that is adapted to receive at least aportion of the product hydrogen stream from the fuel processing systemand to produce an electric current therefrom.

Feedstock delivery system 26 is adapted to receive two or more streams18 and 20 containing components to be delivered to fuel processor 12 asa feed stream 16, and to deliver these components in a predeterminedratio to the fuel processor. Fuel processor 12 is adapted to produce aproduct hydrogen stream 14 containing hydrogen gas from feed stream 16.The fuel cell stack 22 is adapted to produce an electric current fromthe portion of product hydrogen stream 14 delivered thereto. In theillustrated embodiment, a single fuel processor 12 and a single fuelcell stack 22 are shown, however, it should be understood that more thanone of either or both of these components may be used and are within thescope of the present invention. It should also be understood that thesecomponents have been schematically illustrated and that the fuel cellsystem may include additional components that are not specificallyillustrated in the figures, such as feed pumps, air delivery systems,heating assemblies, heat exchangers, and the like.

Fuel processor 12 includes any suitable device that is adapted toproduce hydrogen gas from feed stream 16. Preferably, the fuel processoris adapted to produce substantially pure hydrogen gas, and even morepreferably, the fuel processor is adapted to produce pure hydrogen gas.For the purposes of the present invention, substantially pure hydrogengas is greater than 90% pure, preferably greater than 95% pure, morepreferably greater than 99% pure, and even more preferably greater than99.5% pure. Suitable fuel processors are disclosed in U.S. Pat. Nos.5,997,594, 5,861,137, and 6,221,117, and pending U.S. patent applicationSer. No. 09/802,361, which was filed on Mar. 8, 2001, and is entitled“Fuel Processor and Systems and Devices Containing the Same,” thecomplete disclosures of each of which are incorporated by reference intheir entireties for all purposes.

An illustrative example of a fuel processor 12 is schematicallyillustrated in FIG. 2. As shown, fuel processor 12 includes ahydrogen-producing region 32 in which a stream 36 containing hydrogengas is produced from feed stream 16, such as using one of theabove-described mechanisms. Stream 36 may contain pure hydrogen gas,substantially pure hydrogen gas, or a mixed gas stream containinghydrogen gas and other gases. In embodiments of fuel processor 12 inwhich stream 36 is not of sufficient purity for the intended use of theproduced hydrogen gas, stream 36 may be delivered to a purificationregion 38, in which at least a portion of the other gases are removedfrom stream 36 to produce a purified hydrogen stream 42, and in someembodiments, a byproduct stream 40. In embodiments of fuel processor 12that do not contain a purification region, stream 36 forms producthydrogen stream 14 as it exits the fuel processor. In embodiments havinga purification region, the purified hydrogen stream 42 forms producthydrogen stream 14. It should be understood that fuel processor 12 mayinclude additional filtration or purification regions, such as thoseinvolving chemical and/or mechanical separation of the other gasesand/or impurities from the stream forming product hydrogen stream 14.

In the illustrative embodiment shown in FIG. 2, the above-describedregions are housed in a common shell 48. However, it is within the scopeof the present invention that the fuel processor may be formed without ashell, that the regions may be housed in more than one shell, and thatat least one of the regions may partially or completely extend beyond,or be located external to, shell 48.

In many embodiments, fuel processor 12 will operate at elevatedtemperatures, such as a range between 200° C. and 700° C. Accordingly,fuel processor 12 may include a heating assembly 44, such as shown inFIG. 3. Heating assembly 44 may take any suitable form adapted to heatfuel processor 12, or selected components thereof, to a sufficientoperating temperature. Heating assembly 44 may be included within shell48, or may be located external shell 48 and adapted to deliver heatedfluid streams thereto. In FIG. 3, assembly 44 is schematicallyillustrated partially internal and external shell 48 to represent thatthe heating assembly may be completely within the shell, completelyexternal the shell, or partially within the shell.

Typically, heating assembly 44 will receive a fuel stream 46, such asshown in FIG. 3. Examples of suitable heating assemblies includeelectric heaters 50, such as electric resistance heaters, that receive afuel stream 46 of electrical power and produce heat therefrom to heatthe fuel processor. The electrical power may come from an externalsource, from fuel cell stack 22, from previously stored power from stack22, or combinations thereof.

Another example of a suitable heating assembly 44 is a combustion device52 that contains an ignition source 54 and which combusts a fuel stream46 containing a combustible fuel to produce heat therefrom to heat thefuel processor. Examples of suitable combustion devices 52 includeburners and combustion catalyst beds, which typically are used inconjunction with a combustion chamber or region 55 in which thecombustible fuel is mixed with air. Examples of suitable ignitionsources 54 include a spark plug, glow plug, combustion catalyst, pilotlight, and combinations thereof. Examples of suitable fuel streams 46for a heating assembly that includes a combustion device include one ormore of byproduct stream 40, vented or exhaust gases from fuel processor12 or fuel cell stack 22, and a fuel stream from an external orself-contained source of a combustible fuel, such as propane, gasoline,kerosene, diesel, natural gas, etc. Additional examples includeslipstreams from product hydrogen stream 14, mixed gas stream 36 and/orfeed stream 16.

Also shown in FIG. 3 is an air delivery assembly 56, which is adapted todeliver an air stream 58 to fuel processor 12, such as to combustionregion 55 from which a combustion exhaust stream 59 exits. Air deliveryassembly 56 is schematically illustrated in FIG. 3 and may take anysuitable form. It should be understood that fuel processor 12 and/orheating assembly 44 may be formed without an air delivery assembly 56,such as depending upon the particular mechanism by which the heatingassembly operates.

As discussed with reference to FIG. 1, fuel cell systems 10 according tothe present invention include one or more fuel cell stacks 22 that areadapted to receive product hydrogen stream 14 from fuel processingsystem 11, and more specifically from fuel processor 12. Fuel cell stack22 may receive all of product hydrogen stream 14. Alternatively, some orall of stream 14 may be delivered, via a suitable conduit, for use inanother hydrogen-consuming process, burned for fuel or heat, or storedfor later use.

As schematically illustrated in FIG. 1, fuel cell stack 22 contains atleast one, and typically multiple, fuel cells 24 that are joinedtogether between common end plates 23, which contain fluiddelivery/removal conduits (not shown). Examples of suitable fuel cellsinclude proton exchange membrane (PEM) fuel cells and alkaline fuelcells. Each fuel cell 24 is adapted to produce an electric current fromthe portion of the product hydrogen stream 14 delivered thereto. Thiselectric current may be used to satisfy the energy demands, or appliedload, of an associated energy-consuming device 25. Illustrative examplesof devices 25 include, but should not be limited to, a motor vehicle,recreational vehicle, boat, tools, lights or lighting assemblies,appliances (such as household or other appliances), household, signalingor communication equipment, etc. It should be understood that device 25is schematically illustrated in FIG. 1 and is meant to represent one ormore devices or collection of devices that are adapted to draw electriccurrent from the fuel cell system. By “associated,” it is meant thatdevice 25 is adapted to receive electrical power generated by stack 22.It is within the scope of the invention that this power may be stored,modulated or otherwise treated prior to delivery to device 25.Similarly, device 25 may be integrated with stack 22, or simplyconfigured to draw electric current produced by stack 22, such as viaelectrical power transmission lines.

In FIG. 4, an illustrative example of a fuel cell stack is shown. Stack22 (and the individual fuel cells 24 contained therein) includes ananode region 60 and a cathode region 62, which are separated by anelectrolytic membrane or barrier 64 through which hydrogen ions maypass. The anode and cathode regions respectively include anode andcathode electrodes 66 and 68. Anode region 60 of the fuel cell stackreceives hydrogen stream 14. Cathode region 62 of the fuel cell stack 22receives an air stream 70, and releases a cathode air exhaust stream 72that is partially or substantially depleted in oxygen. Electronsliberated from the hydrogen gas cannot pass through barrier 64, andinstead must pass through an external circuit 74, thereby producing anelectric current that may be used to meet the electrical load applied bythe one or more devices 25, as well as to power the operation of thefuel cell system.

Anode region 60 is periodically purged, and releases a purge stream 76,which may contain hydrogen gas. Alternatively, hydrogen gas may becontinuously vented from the anode region of the fuel cell stack andre-circulated. An electric current is produced by fuel cell stack 22 tosatisfy an applied load, such as from device 25. Also shown in FIG. 3 isan air delivery assembly 78, which is adapted to deliver an air stream82 to fuel cell stack 22, such as to cathode region 62. Air deliveryassembly 78 is schematically illustrated in FIG. 3 and may take anysuitable form. It is within the scope of the present invention that airdelivery assemblies 56 and 78 may be a single device, or separatedevices.

As discussed, feedstock delivery system 26 is adapted to receive streamscontaining the components of feed stream 16 and to form feed stream 16from predetermined ratios of these components. As shown in FIG. 5,system 26 is adapted to receive streams 18 and 20, which respectivelycontain a first feedstock component 84, and a second feedstock component85. System 26 is further adapted to deliver components 84 and 85 in apredetermined mix ratio to fuel processor 12 via feed stream 16. Feedstream 16 and the streams delivering the feedstock components to system26 may be transported by any suitable mechanism, such as by a pumpassembly containing at least one pump or by gravity. Similarly, anysubsequently described intermediate streams may also, be transported bythese or any other suitable mechanism.

It will be understood that while FIG. 5 shows only two streams 18 and 20being delivered to system 26, feedstock delivery system 26 may beadapted to receive more than two streams containing feedstock componentsand to deliver a predetermined mix ratio of those components to the fuelprocessor 12. To illustrate this point, a third stream is shown indashed lines in FIG. 5 at 86 and contains a third feedstock component87. It is within the scope of the present invention that more than threestreams and/or components may be used.

Feedstock components 84 and 85 (and 87) typically will contain one ormore substantially, if not completely, different compositions. Forexample, one of streams 18 and 20 may contain a carbon-containingfeedstock, and the other may contain water. As a further example, one ofstreams 18 and 20 may contain a mixture of two or more carbon-containingfeedstocks, and the other of streams 18 and 20 may contain water. Asstill a further example, one of streams 18, 20 and 86 may contain waterand the other two may contain carbon-containing feedstocks. In yetanother example, one or more of streams 18, 20 (and/or 86) may include acorresponding component 84, 85 (or 87) that is a mixture of two or morecompositions.

It should be understood that the above examples are meant to illustratejust a few of the possible components 84, 85 and 87 that may be usedwith the feedstock delivery system of the present invention, and thatthese examples are not intended to be an exhaustive list of all possiblecombinations and examples. In the following discussion, system 26 willbe described in the context of receiving two streams, namely streams 18and 20, with stream 18 containing a component 84 in the form of acarbon-containing feedstock 88, and stream 20 containing a component 85in the form of water 89, such as shown in FIG. 6.

Examples of suitable carbon-containing feedstocks 88 include at leastone hydrocarbon or alcohol. Examples of suitable hydrocarbons includemethane, propane, natural gas, diesel, kerosene, gasoline and the like.Examples of suitable alcohols include methanol, ethanol, propanol, andpolyols, such as ethylene glycol and propylene glycol.

A single feed stream 16 is shown in FIG. 5, however, it is within thescope of the invention that system 26 may deliver two or more feedstreams 16 to fuel processor 12 and that the feed streams may have thesame or different components. To illustrate this point, a pair of feedstreams 16 are shown in dashed lines in FIG. 5. When thecarbon-containing feedstock is miscible, or soluble, with water, thefeedstock components are typically delivered as a single feed stream 16,such as shown in FIG. 5, or as two or more feed streams having the sameor essentially the same compositions, such as shown in dashed lines inFIG. 5. When the carbon-containing feedstock is immiscible or onlyslightly miscible with water, these components are typically deliveredto fuel processor 12 in separate streams from separate reservoirs orsupplies. In this case, feedstock delivery system 26 may deliver adesired relative amount of the components delivered to system 26separately to fuel processor 12. A benefit of a single feed stream 16 ora plurality of feed streams 16 having the same components is that therelative proportions, or mix ratio, of the components will not varydepending upon the rate at which the stream or streams are delivered tothe fuel processor, or the operation of the pump or other mechanism ormechanisms used to deliver the feed stream or streams, etc. For example,if feed stream 16 is drawn from a reservoir containing a homogenousmixture of the feedstock components, such as components 84 and 85, thenthe predetermined mix ratio is maintained regardless of the rate atwhich the fluid is drawn from the reservoir and/or the number of feedstreams 16 that are drawn from the reservoir.

An additional example of a feed stream 16 that is within the scope ofthe present invention and which may be delivered to fuel processor 12 ina single stream is an emulsion formed from water and one or morecarbon-containing feedstocks 88 that are not miscible with water. Insuch an embodiment, the feedstock delivery system will typically alsoreceive a surfactant 91, either as a separate stream, such as stream 86,or premixed with carbon-containing feedstock 88 or water 89. In FIG. 6,surfactant 91 is indicated in dashed lines to show the latter deliverymechanism. Any suitable surfactant or mixture of surfactants may beused. A feedstock delivery system adapted to produce and deliver a feedstream 16 containing an emulsion will typically include anemulsion-producing device 94, such as a mechanical agitator. It iswithin the scope of the invention that the term “emulsion-producingdevice” is meant to include any suitable powered or non-powered devicethat causes the water and carbon-containing feedstock components tointeract and form an emulsion therefrom. It should similarly beunderstood that in embodiments of system 26 in which the feedstockcomponents are miscible, surfactant 91 and device 94 are not required.

Similar to a carbon-containing feedstock that is miscible with water, anemulsion of a carbon-containing feedstock and water also produces agenerally homogenous mixture of the feedstock components, therebyproducing a stream, or plurality of streams, that will have the same oressentially the same composition regardless of when and from whatlocation the stream is drawn from the feedstock delivery system. In theemulsion- or miscible-embodiments of the feedstock delivery systemdescribed herein, the delivery system may be described as being adaptedto draw and deliver to a fuel processor one or more feed streams 16 froma reservoir containing a generally uniform or homogenous mixture of thefeedstock components, with the drawn streams having the same oressentially the same composition as the liquid in the mixture in thereservoir.

An example of a feedstock delivery system according to the presentinvention that is adapted to receive feedstock components that aremiscible, or soluble, with each other is shown in FIG. 6. In theillustrated embodiment, the feedstock delivery system 26 includes areservoir 90 that is adapted to receive streams containing the feedstockcomponents, such as streams 18 and 20. In the context of a reformer,such as a steam or autothermal reformer, in which one of the componentsis water, then the carbon-containing feedstock should be water-soluble.Nonexclusive examples of water-soluble carbon-containing feedstocksinclude methanol, ethanol, propanol, ethylene glycol and propyleneglycol. Alternatively, the carbon-containing feedstock should form anemulsion with water, such as in the presence of a surfactant 91 and/oragitator or other emulsion-producing device 94.

The feedstock delivery system further includes a sensor assembly 92associated with the reservoir. By “associated,” it is meant that thesensor assembly is adapted to detect one or more predeterminedtriggering events related to, or indicative of, the quantity of one ormore of the feedstock components in the reservoir. Sensor assembly 92includes at least one sensor 93, and in some embodiments will include aplurality of sensors. It is within the scope of the invention that thesensor assembly may be partially within reservoir 90, completely withinreservoir 90, or completely external to reservoir 90. Regardless of theposition of sensor assembly 92 relative to reservoir 90, the sensorassembly is adapted to measure the amount of one or more feedstockcomponents in reservoir 90 and detect the one or more triggering eventsrelated thereto. To provide an example of illustrative configurationsfor sensor assembly 92, FIG. 6 schematically depicts sensor assembly 92internal reservoir 90, FIG. 7 schematically depicts sensor assembly 92partially within and partially external reservoir 90, and FIG. 8schematically depicts sensor assembly 92 external reservoir 90. Itshould be understood that these illustrative configurations are meant toprovide graphical examples of suitable configurations within the scopeof the invention and that feedstock delivery systems according to thepresent invention may have any of these configurations, or others.

A “triggering event” according to the present invention is a measurableevent in which a predetermined threshold value or range of valuesrepresentative of a predetermined amount of one or more of thecomponents forming feed stream 16 is reached or exceeded, therebyindicating that a preselected quantity of the one or more components arepresent in the reservoir. As used herein, “exceeded” is meant to includedeviation from the threshold value or range of values in eitherdirection, such as depending upon the particular threshold event beingmeasured. For example, a threshold event corresponding to the reservoircontaining the predetermined maximum volume of fluid would be exceededwhen more than this volume is added to the reservoir. On the other hand,a triggering event corresponding to the predetermined minimumfluid-level in the reservoir is exceeded when the fluid level dropsbelow this level.

Examples of triggering events include the mass, volume and/or flow ofone or more of the components or of the total mass and/or volume of thecomponents within reservoir 90. Other triggering events are related tothe physical properties of the total liquid, or mixed feedstockcomponents, in the reservoir, such as the refractive index, thermalconductivity, density, viscosity, optical absorbance, and electricalconductivity of the liquid in the reservoir.

The number and type of sensors 93 in a particular sensor assembly are atleast partially determined by the type of triggering event to bedetected. For example, if the triggering event is a predetermined volumeof liquid inside the reservoir, the sensor assembly may include anysuitable device adapted to measure the volume of liquid inside thereservoir. An example of a suitable sensor 93 includes a level detectoror switch, such as a float, optical level detector, and the like. If thetriggering event is a selected mass of liquid inside the reservoir, thesensor assembly may include at least one sensor 93 in the form of asuitable gravimetric measurement device, such as a pressure transduceror a mass transducer. If the triggering event is a selected physicalproperty of the liquid in reservoir 90, suitable sensors include one ormore devices adapted to measure that physical property, such as arefractive index sensor, thermal conductivity sensor, densitometer(density sensor), viscometer (viscosity sensor), spectrophotometer(optical absorbance sensor), or electrical conductivity sensor. Thesesensors may also be used as volumetric sensors by placing the sensor atthe desired volumetric level within reservoir 90. Otherwise, thephysical property sensors will typically be located at a level beneaththe maximum predetermined volume level in the reservoir.

It should be understood that sensor assembly 92 may include a singlesensor or more than one sensor, and may include at least one redundantsensor, i.e., partial or total redundancy of sensors. For example,assembly 92 may include at least one sensor associated with thetriggering event(s) of each component, at least one sensor associatedwith the triggering event(s) of the first component delivered to thereservoir, and/or at least one sensor associated with the triggeringevent(s) of the total amount of liquid in the reservoir.

Responsive to the detection of a triggering event, feedstock deliverysystem 26 is adapted to regulate the flow of the feedstock componentsinto and/or out of reservoir 90 to obtain a predetermined ratio of thecomponents in feed stream 16. Typically, the ratio will be apredetermined molar ratio between the components because it is the molarratio of carbon to oxygen atoms in feed stream 16 that affects theefficiency of fuel processor 12. However, because the desired, orpredetermined, molar ratio and the compositions forming feed stream 16are predetermined, the mix ratio of the components may be expressed inother terms, such as by the relative mass or volume of the components toeach other and/or to the total volume of the components in the reservoiror reservoirs.

For example, in the embodiment of feedstock delivery system 26 shown inFIG. 6, in which feedstock components 88 and 89 (and in some embodiments91) are mixed in a common reservoir 90, the components will typically bedelivered to the reservoir sequentially, and especially when agravimetric or volumetric sensor is used. Accordingly, a first stream 18is delivered to reservoir 90 until a corresponding triggering eventcorresponding to the desired amount of a first feedstock component, suchas carbon-containing feedstock 88 (or other component 84), is detectedby sensor assembly 92. Upon detection of the triggering event, deliveryof stream 18 is halted and delivery of a second feedstock component,such as water (or other component 85), from stream 20, is commenced. Thesecond feedstock component is delivered to reservoir 90 until such timeas the sensor assembly 92 detects a second triggering eventcorresponding to the predetermined amount of the second component. Upondetection of a second triggering event, delivery of the second feedstockcomponent is halted. This cycle may be repeated until all desiredfeedstock components have been delivered to reservoir 90, at which timethe feedstock mix within the reservoir may be delivered to fuelprocessor 12 as one or more feed stream(s) 16. It should be understoodthat the order in which the components are delivered does not matter, solong as the feedstock delivery system is configured to receive thecomponents in the selected order. Because the feed streams are deliveredfrom reservoir 90 and because the feedstock components are miscible witheach other or formed into an emulsion, the predetermined mix ratio willbe maintained regardless of the rate or position at which the feedstream or streams are drawn from the reservoir.

When system 26 includes a mechanical agitator or otheremulsion-producing device, the feedstock components may be constantlyagitated as the components are being added to reservoir 90, agitatedafter the first or second feedstock components are introduced into thereservoir, or agitated after all of the feedstock components have beenadded in their desired amounts. For purposes of brevity, the followingdiscussion will refer to a mixture of a carbon-containing feedstock,such as methanol, that is miscible with water. In the followingdiscussion, it should be understood that a carbon-containing feedstockthat is not miscible with water, such as a hydrocarbon, but forms anemulsion therewith, such as with a surfactant and/or mechanicalagitation, may be used as well.

An example of a sensor assembly 92 adapted to measure triggering eventscorresponding to volumetric measurements is shown in FIG. 7. As shown,reservoir 90 includes a sensor assembly 92 having a plurality of sensors93 that are adapted to detect triggering events corresponding to thevolume of fluid in the reservoir. Sensor assembly 92 includes a firstsensor 93′ adapted to detect when the predetermined volume of a firstfeedstock component is present in the reservoir, and a second sensor 93″to detect when a predetermined volume of a second feedstock component ispresent in the reservoir, namely when the total volume of the componentsin the reservoir reaches a predetermined volume. As discussed, the orderof delivery of the feedstock components may vary, so long as the sensorsare positioned to receive the feed components in the selected order.After the desired amounts of the feedstock components are present in thereservoir, the mixed components may be delivered to a holding tank, ormay be delivered to fuel processor 12. Prior to the delivery of themixed components to the holding tank or fuel processor, the componentsmay be further mixed or agitated to promote the homogeneity of themixture forming feed stream 16.

Sensor assembly 92 may further include a third sensor 93′″ adapted todetect when the reservoir contains less than a predetermined minimumvolume of liquid, thereby indicating that the filling process should berepeated. The minimum fluid level may correspond to when the reservoiris empty. However, because the volumes of sensors 93′, 93″ and 93′″ arepredetermined relative to each other, the order in which the feedstockcomponents will be added and the predetermined mix ratio, the minimumvolume may correspond to some predetermined amount of fluid in thereservoir.

Sensor assembly 92 may, but does not necessarily, include another sensor93′″ that is adapted to detect when the reservoir contains more than apredetermined maximum volume of liquid. Sensor 93′″ indicates a volumegreater than the total predetermined volume of the feedstock components,and as such provides a safety mechanism. More specifically, sensor 93′″only detects a triggering event if the reservoir is nearing or at avolume that exceeds the capacity of the reservoir. Actuation of sensor93′″ may cause one or more of the following: immediate stoppage offeedstock components from being introduced to reservoir 90, immediatestoppage of feed streams 16 from being delivered to fuel processor 12,shut down or idling of fuel processor 12, isolation of fuel cell stack22, and actuation of a user-alert device, such as an alarm, siren,light-emitting device, output on a monitor, etc.

An example of a feedstock delivery system 26 with a sensor assembly 92adapted to measure triggering events corresponding to gravimetric(pressure and/or mass) measurements of the amount of the feedstockcomponents present in reservoir 90 is shown in FIG. 8. As shown,reservoir 90 includes a sensor assembly 92 having a sensor 93 that isadapted to detect triggering events corresponding to the mass orpressure of fluid in the reservoir. Similar to the embodiment discussedin FIG. 6, a first feedstock component is delivered until the sensorassembly detects a triggering event corresponding to a predeterminedamount of the component, and then a second component is delivered untila corresponding second triggering event is detected. In furthersimilarity to the above volumetric-embodiment, the order in which thefeedstock components is delivered may vary, so long as sensor assembly92 is configured to receive the feedstock components in the selectedorder.

The triggering events for a gravimetric system are determined by thedesired mass or pressure of liquid in the reservoir, such as the mass orpressure corresponding to a predetermined amount of the first feedstockcomponent, the mass or pressure corresponding to the combined first andsecond components, etc. When reservoir 90 has a uniform cross-sectionalarea, the mass of liquid in the reservoir is equal to the density of theliquid times the cross-sectional area of the reservoir times the heightof the liquid in the reservoir. The pressure of a liquid measured at thebottom of the reservoir is equal to the density of the liquid times theacceleration of gravity (g) times the height of the liquid in thereservoir. Furthermore, the mass and pressure of a liquid in thereservoir are proportional, in that the mass is equal to the pressuretimes a proportionality constant, namely, the cross-sectional area ofthe reservoir divided by the acceleration of gravity.

In a gravimetric system, the reservoir does not need to be completelyemptied between fillings, or cycles, so long as the sensor assembly, orcontroller associated with the sensor assembly, is zeroed betweencycles. Alternatively, the mass of feedstock components added to thereservoir may be determined by the difference from an initial, orstarting, value obtained prior to delivery of any or a particularfeedstock components. It is within the scope of the invention that thesensor assembly, or controller associated with the controller assembly,may or may not be zeroed between cycles or between the introduction offeedstock components. Because any remaining liquid in reservoir 90 aftera particular cycle contains a homogenous or generally homogenous mixtureof the feedstock components, each fraction of the mixture, including anyresidual amount in the reservoir, should have the same or approximatelythe same compositions. Therefore, if the predetermined amounts of thefeedstock components are added to the reservoir in addition to anyremaining amount of the components, the predetermined mix ratio will bemaintained, subject to the sensor assembly being zeroed, or reset,between fillings and the capacity of the reservoir to contain thepredetermined amounts being added in addition to any residual from theprior cycle. This also applies to a volumetric system, except that thesensors of a volumetric system would need to either be repositioned toaccount to the residual volume of liquid in the reservoir or be presentin sufficient redundancy to have sensors prepositioned for more than onepossible sequential order in which the feedstream components aredelivered to the reservoir.

Advantages of the gravimetric method include the method's insensitivityto temperature and the ease of accurately sensing pressure or weight.Another advantage of the gravimetric method when preparing feedstock fora fuel processor is that the ratio of feed stream components can bechanged while the fuel processor is operating. For example, a controllercan be programmed to change the gravimetric set points for thecarbon-containing feedstock and water (e.g., to increase or decrease theratio of carbon-containing feedstock to water). This change may be inresponse to an external factor, such as an increase in pressure dropthrough the reforming catalyst bed of the fuel processor that indicatescarbon deposition on the catalyst, or it may be programmed to occur atpreset intervals as preventative maintenance. Passing a feed stream 16containing water without carbon-containing feedstock, or a high ratio ofwater to carbon-containing feedstock through the hot reforming catalystbed may be used to remove carbon from reforming catalysts. Furthermore,additional feedstock components may be added to the reservoir withoutmaking changes to the sensor assembly or reservoir.

The controller may also be programmed to supply a high ratio of water tocarbon-containing feedstock to the fuel processor when it is firstoperated following a replacement of the catalyst. This water-richfeedstock mixture allows the activity of the reforming catalyst to beincreased, with the additional water making it less likely that thereforming catalyst will be overheated. The controller may be programmedfor these functions or receive an appropriate user input to deliver thisfeed ratio.

FIG. 7 also provides an example of a feedstock delivery system 26 inwhich the streams containing the feedstock components and the one ormore feed streams 16 are each delivered to or removed from the reservoirthrough separate inputs and outputs. It is within the scope of theinvention, however, that the system may include a manifold 96 throughwhich streams 18 and 20 (and any other streams delivering feedstockcomponents) deliver the components to the reservoir, and through whichone or more feed streams 16 are removed from the reservoir. An exampleof such an embodiment is shown in FIG. 8 for purposes of illustration.Also shown in FIG. 7 are various flow-regulating devices 104, which areshown to illustrate that feedstock delivery systems according to thepresent invention will typically include flow-regulating devices 104 inthe form of valve assemblies 106 to regulate the flow into and/or out ofthe tanks and reservoirs described and illustrated herein. Similarly, aflow-regulating device 104 in the form of a pump 108 is alsoschematically illustrated to demonstrate that pumps may be used totransport the feed streams and feedstock component described herein. Itshould be understood that these flow-regulating devices have beenschematically illustrated to demonstrate examples of suitable devicesand placements for the devices, and that all of the feedstock deliverysystems described herein will incorporate some suitable form offlow-regulating devices. Preferably, some or all of the devicescommunicate with the sensor assemblies so that detection of a triggeringevent causes a predetermined response in at least one correspondingflow-regulating device. Examples of typical responses include causingone or more of the valve assemblies to open or close, and causing a pumpto start or stop pumping fluid. The communication between the sensorassemblies and the flow-regulating devices may be via any suitablemechanical and/or electrical communication.

As discussed, feedstock delivery system 26 is adapted to receive two ormore streams containing feedstock components, optionally mix thesestreams together to form a homogenous or generally uniform mixture ofthe components, and then deliver at least one feed stream 16 to a fuelprocessor 12 containing a predetermined mix ratio of the feedstockcomponents. While the predetermined mix ratio may be measured based onthe volumetric amount of the components to be delivered, the gravimetricamount of the components to be delivered, or the physical properties ofthe mixture of the components to be delivered, these amounts generallyare based upon a preselected molar ratio of carbon and oxygen in feedstream 16. For example, consider a fuel processor in the form of a steamor autothermal reformer in which a carbon-containing feedstock isreacted with water in the presence of a reforming catalyst to producehydrogen gas and various byproducts. If the carbon-containing feedstockis methanol, the ideal reaction stoichiometry is as follows:

CH₃OH+H₂O=CO₂+3H₂

As shown, one mole of water is required for each mole of methanol.Similarly, one mole of water is required for each mole of carbon.Volumetrically, approximately 31-33% water may be mixed withapproximately 67-69% methanol to achieve this mix ratio. This rangeavoids a mix that is deficient in water, namely, a mix that containsless than the ideal stoichiometric amount of water shown in the aboveequation. For example, 4.5 liters of water may be mixed with 10 litersof methanol. Gravimetrically, 18 grams of water may be mixed with 32grams of methanol to achieve this stoichiometric mix ratio (i.e. 64 wt %methanol).

In comparison, the reaction follows the following ideal stoichiometry ifthe carbon-containing feedstock is ethanol:

CH₃CH₂OH+3H₂O=2CO₂+6H₂

As shown, three moles of water are required for each mole of ethanol. Interms of carbon atoms, 1.5 moles of water are required for each mole ofcarbon, or overall, 2 moles of oxygen atoms are required for each moleof carbon. Volumetrically, 54 mL of water may be mixed with 58.3 mL ofethanol at room temperature to produce this stoichiometric mix ratio.Gravimetrically, 54 grams of water may be mixed with 46 grams of ethanolto produce this stoichiometric mix ratio. Of course, these relativevolumetric and gravimetric measurements are provided as illustratedexamples and may be scaled up or down proportionally depending upon suchfactors as the volume of reservoir 90, the desired total volume to beproduced, and/or the rate at which the feed stream is delivered to thefuel processor.

As a further example, consider an emulsion formed from hexane and water,which reacts according to the following ideal stoichiometry in areformer:

C₆H₁₄+12H₂O=6CO₂+19H₂

In terms of carbon atoms, 2 moles of water are required for each mole ofcarbon, or overall, expressed in terms of carbon and oxygen atoms, 2moles of oxygen atoms are required for each mole of carbon.

It is within the scope of the present invention that mix ratios otherthan a stoichiometric mix ratio may be used, including mix ratios thatare greater and lower than the stoichiometric mix ratios describedabove. For a reformer, such as a steam or autothermal reformer, the mixratio is preferably at or above the stoichiometric mix ratio. When lessthan the stoichiometric mix ratio is used, meaning that there is lesswater than the stoichiometric amount of water required per mole ofcarbon, the feed stream may be referred to as being “water lean.” Such afeed stream will tend to produce carbon deposits, or coke, which mayblock the reaction sites on the reforming catalyst and therebyincreasing the pressure drop through the reforming region and/orotherwise decrease the efficiency of the hydrogen-producing region,which typically includes one or more reforming catalyst beds. To guardagainst coke reformation, the feed stream may be “water rich,” whichmeans that the feed stream contains more than the stoichiometric ratioof water to carbon. In fact, it may be periodically desirable to use afeed stream 16 that contains an excess of water (more than 50% greaterthan the stoichiometric mix ratio) to remove accumulated coke. As usedherein, an “excess water” mix ratio refers to a mix ratio that containsat least 50% more water than the stoichiometric mix ratio. It is withinthe scope of the present invention that an excess water mix ratio may be100% extra water, or more. However, a tradeoff with the preventionand/or removal of coke resulting from using excess water is theincreased energy required to vaporize this excess water, therebyincreasing the energy requirements of the reformer. As used herein, theterm “stoichiometric” and “stoichiometry” are used to refer to idealreactions, although it should be understood that the actual reactionsthat occur may differ from the ideal stoichiometry.

In view of the above coke and energy considerations, a reformertypically will be operated with a mix ratio that ranges from thestoichiometric mix ratio to approximately 10-50% greater water on amolar basis than the stoichiometric mix ratio, and for manycarbon-containing feedstocks at a molar mix ratio that ranges from10-25% greater water than the stoichiometric mix ratio. For others, suchas methanol in which coke formation is not as likely to occur, a mixratio that ranges between the stoichiometric mix ratio and 10% greaterwater (on a molar basis), or preferably, 2-4% greater water (on a molarbasis) may be used.

As a still further example of the embodiment described above, when amethanol-water feedstock is used, a desired molar ratio is often 1:1.This molar ratio is obtained by mixing predetermined masses or volumesof methanol or water. As an example, this predetermined ratio isobtained by mixing 10 liters of methanol and 4.5 liters of water.Continuing the above example, when adding methanol to the reservoirbefore water, the sensor assembly may be adapted to detect when thereservoir contains 10 liters of liquid and 14.5 liters of liquid.(Alternatively, when adding water before methanol, the sensor assemblycould be adapted to detect when the reservoir contains 4.5 liters ofliquid and 14.5 liters of liquid.) As will be understood, otherappropriate volumes could be used to obtain the same molar ratio.Volumetrically speaking, a 1:1 molar ratio is approximately 69% methanolto 31% water.

Table 1, below, lists illustrative examples of desired stoichiometricand excess water ratios for mixing water-soluble carbon-containingfeedstocks with water. It is within the scope of the invention, however,that ratios other than those presented in the table may be used. Forexample, in some embodiments, ratios between the listed stoichiometricand excess water ratios may be useful. It is also within the scope ofthe invention that ratios outside of these ratios may be used.

TABLE 1 Exemplary Mix Ratios for Water-Soluble Carbon-ContainingFeedstocks and Water Carbon-Containing Stoichiometric Ratio Excess WaterRatio Feedstock (oxygen:carbon) (oxygen:carbon) Methanol 1:1 2-3:1 Ethanol 2:1 3:1 Ethylene Glycol 2:1 3:1 Propylene Glycol 2:1 3:1For example, for feed streams containing ethanol and water, 58.4 mL ofethanol may be mixed with 54 mL of water to achieve the above-indicatedstoichiometric ratio, and 58.4 mL of ethanol may be mixed with 90 mL ofwater to achieve the above-indicated excess water ratio. For feedstreams containing ethylene glycol and water, 55.8 mL of ethylene glycolmay be mixed with 36 mL water to achieve the above-indicatedstoichiometric ratio and 55.8 mL of ethylene glycol may be mixed with 72mL of water to achieve the above-indicated excess water ratio. For feedstreams containing propylene glycol and water, 73.2 mL of propyleneglycol may be mixed with 72 mL of water to achieve the above-indicatedstoichiometric ratio and 73.2 mL of propylene glycol may be mixed with126 mL of water to achieve the above-indicated excess water ratio. Itshould be understood that system 26 may be adapted to deliver feedstreams containing oxygen:carbon ratios other than the 2:1 and 3:1ratios described above, such as ratios between these values, above thesevalues or below these values. Similarly, molar ratios may be selectedthat are based upon relationships other than moles of oxygen to carbon,such as moles of a particular carbon-containing feedstock to moles ofwater, or moles of a first component to a second component.

As discussed previously, feedstock delivery system 26 adapted to producean emulsion from water and a carbon-containing feedstock that is not (oris only slightly) miscible with water will typically include amechanical agitator or other emulsion-producing device 94. Inembodiments of system 26 in which the feedstock components are misciblewith each other, the reservoir may optionally include one or more mixingdevices 98 that are adapted to promote mixing of the feedstocks, therebygenerating increased homogeneity within the reservoir. Examples ofsuitable mixing devices 98 are static devices 100, such as baffles,helical fins, and the orientation at which the streams containing thefeedstock components are directed into the reservoir. For example,orienting the streams tangential to the sidewalls of the reservoir willpromote mixing within the reservoir. Other examples of mixing devices 98are dynamic devices 102, such as devices that move responsive to theflow of the feedstock compositions striking the device, such as a vaneor other movable baffle, and electrically powered devices that stir theliquid in the reservoir. A benefit of static devices is that they do notrequire power to operate and/or are less prone to failure because oftheir general absence of moving parts. Examples of mixing devices 98 areschematically illustrated in FIGS. 7 and 8. It should be understood thatany of the feedstock delivery systems discussed herein may include amixing device 98, and that the systems shown in FIGS. 7 and 8 may beformed without a mixing device.

From reservoir 90, one or more feed streams 16 may be delivered to fuelprocessor 12 to deliver the feedstock components thereto in thepredetermined mix ratio, such as illustrated in FIGS. 6-8. It is alsowithin the scope of the invention that the mixed feedstock componentsmay be delivered to a holding tank prior to delivery to the reformer orother fuel processor. An example of such a feedstock delivery system isshown in FIG. 9. As shown, stream 110 fluidly connects reservoir 90 to aholding tank 112, which may be any vessel adapted to receive the mixedfeedstock components and from which one or more feed streams 16 may beselectively drawn to deliver the components to fuel processor 12. Stream110, and the other streams discussed herein, may be delivered via anysuitable mechanism, such as by gravity flow, by pumping, etc. Typically,holding tank 112 will have at least as large of a capacity as reservoir90. Tank 112 may also be referred to as a sequential reservoir, in whichcase the feedstock delivery system may be described as having at leasttwo sequential reservoirs adapted to receive and mix the feedstockcomponents prior to delivery of the feed stream in the predetermined mixratio to fuel processor 12.

Transferring the mixed feedstock components to a holding tank prior todelivering the feed streams to fuel processor 12 provides an opportunityto increase the mixing of the feedstock components, such as whileflowing from reservoir 90 to tank 112, as well as when being introducedinto tank 112. For example, because the feedstock components are alreadypresent in the predetermined mix ratio as they are introduced into tank112, any swirling or other agitation of the fluid promotes mixing,whereas no mixing occurs in reservoir 90 until two feedstock componentsare present in the reservoir.

In use, tank 112 enables a batch of mixed feedstock components at thepredetermined mix ratio to be selectively dispensed to fuel processor 12while another batch of feedstock components at a predetermined mix ratiois being prepared. This increases the ability of the fuel cell system orfuel processing system to be able to meet an applied demand, andespecially to do so while maintaining the predetermined mix ratio.

Tank 112 preferably includes a sensor assembly 114 containing at leastone sensor 116 adapted to detect one or more triggering events withinthe tank. Sensor assembly 114 and sensors 116 may have any suitablestructure and location, such as those discussed above with respect toassembly 92 and sensors 93. An example of such a triggering event iswhen the amount of mixed feedstock components in the holding tank isless than a selected minimum amount. For example, a sensor 116′, such asa gravimetric or volumetric sensor, may be used to detect thistriggering event. Similarly, physical property sensors positioned tofunction as level sensors may also be used. Responsive to the detectionof this event, the feedstock delivery system may deliver more mixedfeedstock components from reservoir 90 and/or prepare another batch ofpremixed feedstock components. At least with respect to theabove-described triggering event, a lesser degree of accuracy may beused because the responsiveness of the sensor assembly will not affectthe mix ratio of the feedstock components. Similar to reservoir 90, tank112 may include more than one sensor, such as a sensor 116″ that isadapted to detect a triggering event corresponding to when the volume ofliquid in the tank exceeds a predetermined maximum volume. Responsive todetection of this triggering event, system 26 may stop the flow of mixedfeedstock components from reservoir 90, increase the flow rate ofstreams 16, and/or deliver at least a portion of the feedstockcomponents in reservoir 90 or tank 112 to an auxiliary source, such asan additional holding tank, combustion source, disposal or the like.Tank 112 may, but does not necessarily, include an emulsion-producingdevice 94 and/or mixing device 98, such as schematically illustrated indashed lines in FIG. 9.

In FIGS. 6-9, feedstock delivery system 26 is adapted to fill a singlereservoir 90 with the feedstock components. It is within the scope ofthe invention that system 26 may include more than one reservoir, suchas an embodiment of the system that includes a primary reservoir (suchas reservoir 90) and a secondary or downstream reservoir (such as tank112) into which the contents of the primary reservoir are emptied priorto delivery to fuel processor 12. It is also within the scope of theinvention that the feedstock delivery system may include more than oneprimary reservoir and/or a primary reservoir that is partitioned into aplurality of regions.

For example, in FIG. 10, an embodiment of a feedstock delivery system isshown in which the streams containing the feedstock components are eachdelivered to a separate primary reservoir. For purposes of illustrationthe streams and compositions previously shown and discussed with respectto FIG. 5 are shown in FIG. 10. As discussed, however, stream 86 may beomitted and one of compositions 84 and 85 should include water 89 andthe other should include a carbon-containing feedstock 88. In theillustrated embodiment, system 26 includes reservoirs 90′, 90″ and 90′″,each of which is adapted to receive a predetermined amount of thecorresponding feedstock component and to deliver a stream 110′, 110″ and110′″ containing that component to a secondary reservoir, or holdingtank 112. As shown, each of the primary reservoirs includes a sensorassembly 92 with at least one sensor 93, and holding tank 112 includessensor assembly 114 with at least one sensor 116.

As a variation of the embodiment shown in FIG. 10, the delivery systemmay be formed without tank 112, and feed stream 16 may be formed fromdiscrete streams from each reservoir that are delivered as a unit tofuel processor 12. Such an embodiment is suitable for use in which thefeedstock components are not miscible and are not formed into anemulsion. In such an embodiment, the streams are preferably, but notnecessarily, delivered via a mechanism in which the relative flow rateof each stream is controlled to correspond to the relative flow rates ofthe other streams, thereby maintaining the predetermined mix ratio eventhough the streams contain different components that are not mixed untildelivery to fuel processor 12. An example of such a mechanism is a dual-or multi-headed pump, such as disclosed in copending U.S. patentapplication Ser. No. 09/190,917, which was filed on Nov. 12, 1998, isentitled “Fuel Cell System,” and the complete disclosure of which ishereby incorporated by reference for all purposes.

In FIG. 11, an embodiment of a partitioned reservoir 90 is shown andgenerally indicated at 120. As shown, reservoir 120 includes a partition122 that separates the reservoir into a pair of regions 124 and 126.Unless otherwise discussed, each of the reservoirs disclosed herein (andregions thereof) may include a sensor assembly 92 having one or moresensors 93 adapted to detect one or more selected triggering events.Preferably, at least region 124 is sized to correspond to the amount ofthe first feedstock component to be added to the reservoir. Thisselective sizing of the reservoir enables greater accuracy in avolumetric measurement because the volume of the first feedstockcomponent may be measured at a conduit, or neck portion, 128 thatinterconnects the regions and which has a reduced cross-sectional areacompared to regions 124 and 126. When sensor assembly 92 is adapted todetect triggering events corresponding to volumetric measurements, itmay be desirable for both of the regions to be sized to correspond tothe volume of fluid to be contained therein for the predetermined mixratio and to include a conduit or neck portion 128 of reducedcross-sectional area in which the volumetric measurements are made.Reservoir 120 may alternatively be described as a pair of primaryreservoirs that are fluidly connected so that liquid overflowing fromthe first reservoir (90′) flows into the second reservoir (90″).

For example, as stated above, the desired methanol-water molar ratio isoften 1:1 and this ratio is obtainable by mixing 10 liters of methanolwith 4.5 liters of water. Thus, when adding methanol before water,region 124 may have a 10-liter capacity and region 126 may have a4.5-liter capacity. In this embodiment, the sensor assembly may includevolumetric sensors 93, such as level indicators, positioned at the topof each region, indicating when each portion is filled. As will beappreciated, the regions may have capacities other than those discussedabove, so long as the predetermined mix ratio is obtainable. Forexample, at least one of the regions may have a capacity that exceedsthe desired volume of liquid to be received in the region. In such anembodiment, a sensor or sensor assembly associated with that region maybe positioned to measure when the desired volume has been achieved.

In FIG. 11, reservoir 120 (and 90″) is shown including a vent 130through which excess fluid in the reservoir may be exhausted. Vent 130may exhaust any feedstock components passing thereto to the environment,or deliver the components to a combustion source. However, vent 130preferably forms a portion of a self-contained spill-prevention assembly132. By “self-contained,” it is meant that the spill-prevention assemblyis adapted to deliver, via an overflow stream 136, any fluid passingtherethough to a containment structure. For example, overflow stream 136may deliver any fluid passing therethrough to a spill tank, such as atank 134 that is configured solely to contain waste or vented feedstockcomponents, to mix tank 112, or to fuel processor 12. A benefit of adedicated disposal unit, such as spill tank 134 is that the ventedfeedstock components are not introduced into the fuel processor.However, and especially when system 26 is adapted to detect a triggeringevent in the form of a flow of feedstock components in vent stream 136,the amount of feedstock components in stream 136 should typically befairly small and therefore should have only a negligible effect on thepredetermined mix ratio.

Feedstock delivery systems 26 according to the present invention may,but do not necessarily, include a controller 140. Controller 140 isadapted to monitor selected operating parameters such as detection ofthe preselected triggering event(s) by the sensor assembly in thefeedstock delivery system and/or the pressures, temperatures, and flowrates of the fuel cell or fuel processing system and direct the relativeflow of the feedstock components and feed stream 16 to and from thefeedstock delivery system 26 at least partially in response to monitoredvalues. An example of a controller is schematically illustrated in FIG.12. As shown, controller 140 includes a processor 142, whichcommunicates with sensors 144 and controlled-devices 1-46 viacommunication linkages 148. Communication linkage 148 may be anysuitable wired or wireless mechanism for one- or two-way communicationbetween the corresponding devices, such as input signals, commandsignals, measured parameters, etc.

Illustrative examples of controlled devices 146 include theflow-regulating devices 104 discussed herein, such as valves and pumps.Other examples include compressors, heating assemblies, fuel processor12, and fuel cell stack 22. Illustrative examples of sensors 144 includesensors 93 and/or 116. However, processor 142 may communicate withadditional sensors 144, such as to monitor other operating conditions ofthe feedstock delivery system and/or other components of the fuelprocessing or fuel cell system. Similarly, the processor may communicatewith various sensors adapted to measure the compositions of one or morestreams to determine whether the measured composition corresponds to theexpected composition. In addition to the sensors described above, otherexamples of suitable sensors include temperature sensors, ammeters, andsensors adapted to measure the composition of a particular stream.

Processor 142 may have any suitable form, such as including acomputerized device, software executing on a computer, an embeddedprocessor, programmable logic controllers or functionally equivalentdevices. The controller may also include any suitable software,hardware, or firmware. For example, the controller may include a memorydevice 150 in which preselected, preprogrammed and/or user-selectedoperating parameters are stored. The memory device may include avolatile portion, nonvolatile portion, or both.

It should be understood that the particular form of communicationbetween the processor, sensors and controlled elements may take anysuitable configuration. For example, the sensors may constantly orperiodically transmit measured values to the processor, which comparesthese measured values to stored threshold values or ranges of values todetermine if the measured value exceeds a preprogrammed or stored valueor range of values. If so, the processor may send a command signal toone or more of the controlled devices. In another example, the sensorsthemselves may measure an operating parameter and compare it to a storedor predetermined threshold value or range of values and send a signal tothe processor only if the measured value exceeds the stored value orrange of values. By “exceeds,” it is meant that the measured valuedeviates from the preselected or stored value or range of values ineither direction, and that this deviation may alternatively include aselected tolerance, such as a deviation by more than 5%, 10%, 25%, etc.

Examples of operating parameters measured by the sensors include theabove-discussed triggering events. Preferably, the controller's memorydevice includes threshold values or ranges of values corresponding tomore than one set of triggering events. For example, for a particularset of feedstock components, the controller may contain threshold valuescorresponding to the stoichiometric mix ratio, excess water mix ratio,and perhaps additional mix ratios between or beyond these ratios.Responsive to user inputs to the subsequently described user interface,or to measured parameters detected by the sensors, the controller mayswitch between these stored mix ratios and corresponding thresholdvalues. Similarly, the controller may include one or more sets ofthreshold values or ranges of values for the set of feedstock componentswhen the components are delivered to the feedstock delivery system in adifferent order. As another example, the controller may include one ormore sets of threshold values or ranges of value corresponding to adifferent set of feedstock components. Each of these sets of thresholdvalues may be stored in the controller's memory device.

Another example of an operating parameter to be measured by controller140 is the time it takes for various amounts of the feedstock componentsand/or the intermediate or feed streams to travel into, within, or outof feedstock delivery system 26. More specifically, controller 140 mayprovide an additional safety check by measuring the time it takes for apredetermined amount of liquid to flow within the feedstock deliverysystem and comparing this time to a stored threshold value. The time maybe measured, for example, from when a flow-regulating device 104 isactuated to begin the flow of the liquid, and when a triggering eventcorresponding to the predetermined amount of the liquid being presentshould be received. If this time is exceeded, or exceeded by more than aselected tolerance, then this time period itself becomes a triggeringevent indicative of a malfunction within the feedstock delivery system.

As discussed, the operation of system 26 may be controlled at least inpart by the measured parameters detected by sensors 144. The processorcompares the measured parameters to the stored threshold values, and ifone or more measured parameters exceeds its corresponding thresholdvalue or range of values, the processor sends a control signal to one ormore controlled devices 146 within the feedstock delivery system, and/orwithin the complete fuel cell or fuel processing system.

Controller 140 may also include a user interface through which a usermay monitor and/or interact with the operation of the controller. Anexample of a user interface is shown in FIG. 13 and indicated generallyat 150. As shown, interface 150 includes a display region 152 with ascreen 154 or other suitable display mechanism in which information ispresented to the user. For example, display region 152 may display thecurrent values measured by one or more of sensors 142, the currentoperating parameters of the system, the stored threshold values orranges of values. Previously measured values may also be displayed.Other information regarding the operation and performance of the fuelprocessing system may also be displayed in region 152.

User interface 150 may also include a user input device 156 throughwhich a user communicates with, such as by sending commands to, thecontroller. For example, input device 156 may enable a user to inputcommands to change the operating state of the fuel processing of thefuel cell system, to change the mix ratio to be used, the order in whichthe feedstock components are delivered to the feedstock delivery system,to change one or more of the stored threshold values and/or operatingparameters of the system, and/or to request information from thecontroller about the previous or current operating parameters of thesystem. Input device 156 may include any suitable device for receivinguser inputs, including rotary dials and switches, push-buttons, keypads,keyboards, a mouse, touch screens, etc. Also shown in FIG. 13 is auser-signaling device 158 that alerts a user when an acceptablethreshold level has been exceeded. Device 158 may include an alarm,lights, or any other suitable mechanism or mechanisms for alertingusers.

It should be understood that it is within the scope of the presentinvention that the feedstock delivery system may include a controllerwithout a user interface, and that it is not required for the userinterface to include all of the elements described herein. The elementsdescribed above have been schematically illustrated in FIG. 13collectively, however, it is within the scope of the present inventionthat they may be implemented separately. For example, the user interfacemay include multiple display regions, each adapted to display one ormore of the types of user information described above. Similarly, asingle user input device may be used, and the input device may include adisplay that prompts the user to enter requested values or enables theuser to toggle between input screens.

In FIG. 14, controller 140 is shown being in communication with sensorassemblies 92 and 114. Controller 140 may also be in communication withvarious sensors 144 located throughout fuel processing system 11 and thefuel cell system 10. As will be understood, controller 140 may belocated within, external to, or partially within and partially externalto feed stock delivery system 26.

It should be understood that the flow-regulating devices shown in FIG.14 may be, but are not necessarily, controlled devices within the scopeof the present invention. For example, valves 106 are shown associatedwith control supply streams 18 and 20, intermediate stream 110 and feedstream 16. Controller 140 may communicate with and control valves 106,as well as sensor assemblies 92 and 114. In addition, controller 140 maycontrol mix pump 108. System 10 may include less than all of thesecommunication lines, and may also include many more lines ofcommunication throughout the fuel cell system. Controller 140 may directthe mixing and delivery of the feedstock to the fuel processor systemusing the above-described system.

An example of a suitable fuel processor 12 suitable for use in systems10 and 11 is a steam reformer. An example of a suitable steam reformeris shown in FIG. 15 and indicated generally at 230. Reformer 230includes a hydrogen-producing region 32 that includes a steam reformingcatalyst 234. In the context of a steam reformer, hydrogen-producingregion 32 may be referred to as a reforming region. Alternatively,reformer 230 may be an autothermal reformer that includes an autothermalreforming catalyst. In reforming region 32, a mixed gas stream 36containing hydrogen gas and other gases is produced from feed stream 16.In the context of a steam reformer, stream 36 may also be referred to asa reformate stream. Stream 36 is delivered to a separation region, orpurification region, 38, where the hydrogen gas is purified. Inseparation region 38, the hydrogen-containing stream is separated intoone or more byproduct streams, which are collectively illustrated at 40,and a hydrogen-rich stream 42 by any suitable pressure-driven separationprocess. In FIG. 15, hydrogen-rich stream 42 is shown forming producthydrogen stream 14.

An example of a suitable structure for use in separation region 38 is amembrane module 244, which contains one or more hydrogen-selective metalmembranes 246. Examples of suitable membrane modules formed from aplurality of hydrogen-selective metal membranes are disclosed in U.S.patent application Ser. No. 09/291,447, which was filed on Apr. 13,1999, is entitled “Fuel Processing System,” and the complete disclosureof which is hereby incorporated by reference in its entirety for allpurposes. In that application, a plurality of generally planar membranesare assembled together into a membrane module having flow channelsthrough which an impure gas stream is delivered to the membranes, apurified gas stream is harvested from the membranes and a byproductstream is removed from the membranes. Gaskets, such as flexible graphitegaskets, are used to achieve seals around the feed and permeate flowchannels. Also disclosed in the above-identified application are tubularhydrogen-selective membranes, which also may be used. Other suitablemembranes and membrane modules are disclosed in U.S. patent applicationSer. No. 09/618,866, which was filed on Jul. 19, 2000 and is entitled“Hydrogen-Permeable Metal Membrane and Method for Producing the Same,”and U.S. patent application Ser. No. 09/812,499, which was filed on Mar.19, 2001 and is entitled “Hydrogen-Selective Metal Membrane Modules andMethod of Forming the Same,” the complete disclosures of which arehereby incorporated by reference in their entireties for all purposes.Other suitable fuel processors are also disclosed in the incorporatedpatent applications.

The thin, planar, hydrogen-permeable membranes are preferably composedof palladium alloys, most especially palladium with 35 wt % to 45 wt %copper. These membranes, which also may be referred to ashydrogen-selective membranes, are typically formed from a thin foil thatis approximately 0.001 inches thick. It is within the scope of thepresent invention, however, that the membranes may be formed fromhydrogen-selective metals and metal alloys other than those discussedabove, hydrogen-permeable and selective ceramics, or carboncompositions. The membranes may have thicknesses that are larger orsmaller than discussed above. For example, the membrane may be madethinner, with commensurate increase in hydrogen flux. Thehydrogen-permeable membranes may be arranged in any suitableconfiguration, such as arranged in pairs around a common permeatechannel as is disclosed in the incorporated patent applications. Thehydrogen permeable membrane or membranes may take other configurationsas well, such as tubular configurations, which are disclosed in theincorporated patents.

Another example of a suitable pressure-separation process for use inseparation region 38 is pressure swing absorption (PSA). In a pressureswing adsorption (PSA) process, gaseous impurities are removed from astream containing hydrogen gas. PSA is based on the principle thatcertain gases, under the proper conditions of temperature and pressure,will be adsorbed onto an adsorbent material more strongly than othergases. Typically, it is the impurities that are adsorbed and thusremoved from reformate stream 36. The success of using PSA for hydrogenpurification is due to the relatively strong adsorption of commonimpurity gases (such as CO, CO₂, hydrocarbons including CH₄, and N₂) onthe adsorbent material. Hydrogen adsorbs only very weakly and sohydrogen passes through the adsorbent bed while the impurities areretained on the adsorbent. Impurity gases such as NH₃, H₂S, and H₂Oadsorb very strongly on the adsorbent material and are therefore removedfrom stream 36 along with other impurities. If the adsorbent material isgoing to be regenerated and these impurities are present in stream 36,separation region 38 preferably includes a suitable device that isadapted to remove these impurities prior to delivery of stream 36 to theadsorbent material because it is more difficult to desorb theseimpurities.

Adsorption of impurity gases occurs at elevated pressure. When thepressure is reduced, the impurities are desorbed from the adsorbentmaterial, thus regenerating the adsorbent material. Typically, PSA is acyclic process and requires at least two beds for continuous (as opposedto batch) operation. Examples of suitable adsorbent materials that maybe used in adsorbent beds are activated carbon and zeolites, especially5 Å (5 angstrom) zeolites. The adsorbent material is commonly in theform of pellets and it is placed in a cylindrical pressure vesselutilizing a conventional packed-bed configuration. It should beunderstood, however, that other suitable adsorbent materialcompositions, forms and configurations may be used.

Reformer 230 may, but does not necessarily, further include a polishingregion 252, such as shown in FIG. 16. Polishing region 252 receiveshydrogen-rich stream 42 from separation region 38 and further purifiesthe stream by reducing the concentration of, or removing, selectedcompositions therein. For example, when stream 42 is intended for use ina fuel cell stack, such as stack 22, compositions that may damage thefuel cell stack, such as carbon monoxide and carbon dioxide, may beremoved from the hydrogen-rich stream. Region 252 includes any suitablestructure for removing or reducing the concentration of the selectedcompositions in stream 42. For example, when the product stream isintended for use in a PEM fuel cell stack or other device that will bedamaged if the stream contains more than determined concentrations ofcarbon monoxide or carbon dioxide, it may be desirable to include atleast one methanation catalyst bed 254. Bed 254 converts carbon monoxideand carbon dioxide into methane and water, both of which will not damagea PEM fuel cell stack. Polishing region 252 may also include anotherhydrogen-producing device 256, such as another reforming catalyst bed,to convert any unreacted feedstock into hydrogen gas. In such anembodiment, it is preferable that the second reforming catalyst bed isupstream from the methanation catalyst bed so as not to reintroducecarbon dioxide or carbon monoxide downstream of the methanation catalystbed.

In FIGS. 15 and 16, reformer 230 is shown including a shell 48 in whichthe above-described components are contained. Shell 48, which also maybe referred to as a housing, enables the fuel processor, such asreformer 230, to be moved as a unit. It also protects the components ofthe fuel processor from damage by providing an exterior cover andreduces the heating demand of the fuel processor because the componentsof the fuel processor may be heated as a unit, and heat generated by onecomponent may be used to heat other components. Shell 48 may, but doesnot necessarily, include an interior layer of an insulating material250, such as a solid insulating material or an air-filled cavity. It iswithin the scope of the invention, however, that the reformer may beformed without a housing or exterior shell, or alternatively, that oneor more of the components may either extend beyond the shell or belocated external the shell. For example, and as schematicallyillustrated in FIG. 15, polishing region 252 may be external shell 48and/or a portion of reforming region 32 may extend beyond the shell.Other examples of fuel processors demonstrating these configurations areillustrated in the incorporated references.

Fuel cell systems 10 according to the present invention may be combinedwith an energy-consuming device, such as device 25, to provide thedevice with an integrated, or on-board, energy source. Examples of suchdevices include a motor vehicle, such as a recreational vehicle,automobile, boat or other seacraft, and the like, a dwelling, such as ahouse, apartment, duplex, apartment complex, office, store or the like,or self-contained equipment, such as a microwave relay station,transmitting assembly, remote signaling or communication equipment, etc.

Finally, it is within the scope of the invention that theabove-described fuel processor and feedstock delivery system may be usedindependent of a fuel cell stack. In such an embodiment, the system maybe referred to as a fuel processing system and may be used to provide asupply of pure or substantially pure hydrogen. This supply may bestored, delivered to an integrated or separate hydrogen-consumingdevice, or otherwise used.

INDUSTRIAL APPLICABILITY

The present invention is applicable in any fuel processing system orfuel cell system in which hydrogen gas is produced from a feed streamthat includes at least two components.

It is believed that the disclosure set forth above encompasses multipledistinct inventions with independent utility. While each of theseinventions has been disclosed in its preferred form, the specificembodiments thereof as disclosed and illustrated herein are not to beconsidered in a limiting sense as numerous variations are possible. Thesubject matter of the inventions includes all novel and non-obviouscombinations and subcombinations of the various elements, features,functions and/or properties disclosed herein. Where the disclosure orsubsequently filed claims recite “a” or “a first” element or theequivalent thereof, it should be within the scope of the presentinventions that such disclosure or claims may be understood to includeincorporation of one or more such elements, neither requiring norexcluding two or more such elements.

Applicants reserve the right to submit claims directed to certaincombinations and subcombinations that are directed to one of thedisclosed inventions and are believed to be novel and non-obvious.Inventions embodied in other combinations and subcombinations offeatures, functions, elements and/or properties may be claimed throughamendment of those claims or presentation of new claims in that or arelated application. Such amended or new claims, whether they aredirected to a different invention or directed to the same invention,whether different, broader, narrower or equal in scope to the originalclaims, are also regarded as included within the subject matter of theinventions of the present disclosure.

1. A hydrogen-producing fuel processing system, comprising: a fuelprocessor having a hydrogen-producing region adapted to produce a streamcomprising hydrogen gas as a majority component from a feed streamcomprising water and a carbon-containing feedstock; a heating assemblyadapted to receive and combust a fuel stream to produce a combustionexhaust stream for heating at least the hydrogen-producing region to ahydrogen-producing operating temperature of at least 250° C.; afeedstock delivery system comprising a reservoir and a pump assembly,wherein the reservoir contains a liquid mixture that consistsessentially of at least 31 vol % water and the carbon-containingfeedstock; wherein the pump assembly includes at least one pump adaptedto draw liquid mixture from the reservoir as the feed stream and todeliver the feed stream to the hydrogen-producing region; and furtherwherein the pump assembly includes at least one pump adapted to drawliquid mixture from the reservoir as at least a portion of the fuelstream and to deliver the fuel stream to the heating assembly.
 2. Thefuel processing system of claim 1, wherein the feedstock delivery systemfurther comprises a sensor assembly adapted to measure the amount of atleast one of the water, the carbon-containing feedstock, and the liquidmixture in the reservoir and to detect at least one triggering eventrelated to the amount.
 3. The fuel processing system of claim 2, whereinthe feedstock delivery system is adapted to regulate operation of thepump assembly responsive to inputs from the sensor assembly.
 4. The fuelprocessing system of claim 2, wherein the sensor assembly is adapted todetect at least one triggering event related to the gravimetric quantityof one or more of the feedstock components in the reservoir.
 5. The fuelprocessing system of claim 2, wherein the sensor assembly is adapted todetect at least one triggering event related to the volumetric quantityof one or more of the feedstock components in the reservoir.
 6. The fuelprocessing system of claim 1, wherein the carbon-containing feedstock ismiscible in water.
 7. The fuel processing system of claim 1, wherein thereservoir includes a mixing device adapted to promote mixing of thecarbon-containing feedstock and the water in the reservoir.
 8. The fuelprocessing system of claim 1, wherein the carbon-containing feedstock isselected to form an emulsion with water, and further wherein thefeedstock delivery system includes an emulsion-producing device adaptedto produce an emulsion of the water and the carbon-containing feedstock.9. The fuel processing system of claim 1, wherein the liquid mixturecontains the water and the carbon-containing feedstock in apredetermined steam-to-carbon ratio.
 10. The fuel processing system ofclaim 1, wherein the liquid mixture contains the water and thecarbon-containing feedstock in a predetermined steam-to-carbon ratio inthe range of 1:1-1.5:1.
 11. The fuel processing system of claim 1,wherein the liquid mixture contains the water and the carbon-containingfeedstock in a predetermined steam-to-carbon ratio that is greater than1:1.
 12. The fuel processing system of claim 1, wherein thehydrogen-producing region contains a steam reforming catalyst adapted toproduce the stream containing hydrogen gas as a majority component bycatalytic reaction of the feed stream at the hydrogen-producingoperating temperature.
 13. The fuel processing system of claim 1,wherein the at least one pump adapted to draw liquid mixture from thereservoir as the feed stream and to deliver the feed stream to thehydrogen-producing region and the at least one pump adapted to drawliquid mixture from the reservoir as at least a portion of the fuelstream and to deliver the fuel stream to the heating assembly are thesame pump.
 14. The fuel processing system of claim 1, wherein the atleast one pump adapted to draw liquid mixture from the reservoir as thefeed stream and to deliver the feed stream to the hydrogen-producingregion and the at least one pump adapted to draw liquid mixture from thereservoir as at least a portion of the fuel stream and to deliver thefuel stream to the heating assembly are different pumps.
 15. The fuelprocessing system of claim 1, wherein the fuel processing system furtherincludes a purification region adapted to receive the stream containinghydrogen gas and to produce therefrom a product hydrogen streamcontaining at least substantially pure hydrogen gas and a byproductstream containing a reduced concentration of hydrogen gas than thestream containing hydrogen gas.
 16. The fuel processing system of claim15, wherein the purification region includes a pressure swing adsorptionassembly.
 17. The fuel processing system of claim 15, wherein thepurification region includes at least one hydrogen-selective membrane.18. The fuel processing system of claim 1, wherein the fuel processingsystem includes means for vaporizing the feed stream.
 19. The fuelprocessing system of claim 1, wherein the fuel processing system furtherincludes a fuel cell stack adapted to receive at least a portion of thestream containing hydrogen gas and to produce an electric currenttherefrom.
 20. A method for producing hydrogen gas by catalytic reactionof water and a carbon-containing feedstock, the method comprising:drawing, from a supply containing a liquid mixture consistingessentially of at least 31 vol % water and the carbon-containingfeedstock, a feed stream of the liquid mixture; combusting the fuelstream to produce a combustion exhaust stream; heating ahydrogen-producing region of a fuel processor with the combustionexhaust stream to a hydrogen-producing operating temperature of at least250° C.; drawing a feed stream of the liquid mixture from the supply;delivering at least a portion of the feed stream to a hydrogen-producingregion of a fuel processor; and producing a stream containing hydrogengas as a majority component from the portion of the feed stream.